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1.
Evaluation of Mixing-Height Retrievals from Automatic Profiling Lidars and Ceilometers in View of Future Integrated Networks in Europe 总被引：2，自引：0，他引：2
M. Haeffelin F. Angelini Y. Morille G. Martucci S. Frey G. P. Gobbi S. Lolli C. D. O’Dowd L. Sauvage I. Xueref-Rémy B. Wastine D. G. Feist 《Boundary-Layer Meteorology》2012,143(1):49-75
The determination of the depth of daytime and nighttime mixing layers must be known very accurately to relate boundary-layer concentrations of gases or particles to upstream fluxes. The mixing-height is parametrized in numerical weather prediction models, so improving the determination of the mixing height will improve the quality of the estimated gas and particle budgets. Datasets of mixing-height diurnal cycles with high temporal and spatial resolutions are sought by various end users. Lidars and ceilometers provide vertical profiles of backscatter from aerosol particles. As aerosols are predominantly concentrated in the mixing layer, lidar backscatter profiles can be used to trace the depth of the mixing layer. Large numbers of automatic profiling lidars and ceilometers are deployed by meteorological services and other agencies in several European countries providing systems to monitor the mixing height on temporal and spatial scales of unprecedented density. We investigate limitations and capabilities of existing mixing height retrieval algorithms by applying five different retrieval techniques to three different lidars and ceilometers deployed during two 1-month campaigns. We studied three important steps in the mixing height retrieval process, namely the lidar/ceilometer pre-processing to reach sufficient signal-to-noise ratio, gradient detection techniques to find the significant aerosol gradients, and finally quality control and layer attribution to identify the actual mixing height from multiple possible layer detections. We found that layer attribution is by far the most uncertain step. We tested different gradient detection techniques, and found no evidence that the first derivative, wavelet transform, and two-dimensional derivative techniques have different skills to detect one or multiple significant aerosol gradients from lidar and ceilometer attenuated backscatter. However, our study shows that, when mixing height retrievals from a ultraviolet lidar and a near-infrared ceilometer agreed, they were 25?C40% more likely to agree with an independent radiosonde mixing height retrieval than when each lidar or ceilometer was used alone. Furthermore, we point to directions that may assist the layer attribution step, for instance using commonly available surface measurements of radiation and temperature to derive surface sensible heat fluxes as a proxy for the intensity of convective mixing. It is a worthwhile effort to pursue such studies so that within a few years automatic profiling lidar and ceilometer networks can be utilized efficiently to monitor mixing heights at the European scale. 相似文献
2.
Christoph Münkel Noora Eresmaa Janne Räsänen Ari Karppinen 《Boundary-Layer Meteorology》2007,124(1):117-128
The Vaisala ceilometers CT25K and CL31 are eye-safe single lens lidar systems reporting attenuated backscatter profiles; they
often operate 24 h a day in fully automated, hands-off operation mode. These profiles can be used for more than just cloud-base
height determination. In dry weather situations, there is a fairly good correlation between the ceilometer near-range backscatter
and in situ PM10 concentration readings. The comparison of mixing height values based on soundings and on ceilometer backscattering
profiles indicates that ceilometers are suitable instruments for determining the convective mixing height. Its enhanced optics
and electronics enables the CL31 ceilometer to detect fine boundary-layer structures whose counterparts are seen in temperature
profiles. 相似文献
3.
D. N. Asimakopoulos C. G. Helmis J. Michopoulos 《Meteorology and Atmospheric Physics》2004,85(1-3):85-92
Summary It is the purpose of this paper to evaluate the different Sodar approaches and methods for the determination of the atmospheric mixing height against direct measurements. To achieve this objective a specific experiment was designed and performed incorporating, a research home made Sodar, a tethered balloon and a radiosonde facility as well as a conventional ground based meteorological station. The obtained data were statistically treated and analyzed to high-light the advantages and disadvantages of the various methods during different meteorological conditions. The results indicate that all three manual methods produce reasonable estimates during convective conditions, while for the stable cases the acceptable techniques are reduced to two. For the automated approach however, the two methods produced quite acceptable estimates during convective conditions, while for the stable cases none was found suitable for use. 相似文献
4.
多普勒声雷达测风与直接测量仪器的观测比较 总被引：3，自引：0，他引：3
文中对多普勒声雷达测风和325 m铁塔上风速、风向仪及超声风速仪的测量值进行了观测比较。结果表明,当信噪比大于1时,两种方法测量的平均风速、风向的相关较好,风速、风向廓线较为接近;声雷达测量的垂直风速平均值和均方根差比超声风速仪的测量值略偏大。这与国外进行的观测比较结果一致。 需要指出,声雷达和直接测量仪器的观测比较中存在一定差异,特别是对比每一次的观测值就可以看出,在某些情况下还存在明显差异。进一步分析声雷达测风产生偏差的原因,对误差做出合理的订正是十分必要的。 相似文献
5.
In order to study the turbulence structure behind a multiscale tree-like element in a boundary layer, detailed particle image
velocimetry measurements are carried out in the near-wake of a fractal-like tree. The tree is a pre-fractal with five generations,
each consisting of three branches and a scale-reduction factor of 1/2 between consecutive generations. Detailed mean velocity
and turbulence stress profiles are documented, as well as their downstream development. Scatter plots of mean velocity gradient
(transverse shear in the wake) and Reynolds shear stress exhibit a good linear relation at all locations in the flow. Therefore,
in the transverse direction of the wake evolution, the data support the Boussinesq eddy-viscosity concept. The measured mixing
length increases with streamwise distance, in agreement with classic wake expansion rates. Conversely, the measured eddy viscosity
and mixing length in the transverse direction decrease with increasing elevation, which differs from the behaviours measured
in the vertical direction in traditional boundary layers or in canopy flows studied before. In order to find an appropriate
single length scale to describe the wake evolution behind a multiscale object, two models are proposed, based on the notion
of superposition of scales. One approach is based on the radial spectrum of the object while the second is based on its length-scale
distribution evaluated using fractal geometry tools. Both proposed models agree well with the measured mixing length. The
results suggest that information about multiscale clustering of branches must be incorporated into models of the mixing length
for flows through single or sparse canopies of multiscale trees. 相似文献
6.
Frank Beyrich 《Boundary-Layer Meteorology》1995,74(1-2):1-18
Sodar has been used for about 20 years to determine mixing height. However, estimation of the height of a convective boundary layer (CBL) that exceeds the sodar-probing range is still an unsolved question. As one possible way, it is suggested that one adapt a simple mixed-layer model to sodar observations during the morning growth period of the CBL, when its top can be clearly detected. Results are compared with other methods for CBL-height estimation from sodar data that have been proposed in the literature. Finally, some prognostic aspects are discussed. 相似文献
7.
毫米波云雷达与激光云高仪观测数据对比分析 总被引：3，自引：2，他引：1
2013年5月1日至6月8日,中国气象局气象探测中心在中国气象局大气探测综合试验基地进行了云高观测试验,试验仪器包括:(1)毫米波云雷达(35 GHz),观测数据为回波功率值,时间分辨率1 min;(2)激光云高仪,观测数据为后向散射光强度,时间分辨率为1 min;本工作对39天试验数据进行对比分析,结果表明:毫米波云雷达数据获取率要比激光云高仪的数据获取率高26%;在雾霾天气时激光云高仪的数据获取率比毫米波云雷达低51%;降水天气对激光云高仪测量云底高度的结果影响较大,对云雷达的测量的结果影响较小;毫米波云雷达和激光云高仪测得云底高度平均相差不超过300 m,比较接近。 相似文献
8.
P. S. Anderson 《Boundary-Layer Meteorology》2003,107(2):323-351
Co-located high resolution profiles of acoustic backscatter,wind vector and potential temperature are presented, measured within the stable atmosphericboundary layer over an Antarctic ice shelf. Acoustic profiles from a monostaticacoustic radar (Sodar) indicate complex structure within the boundary layer, whilstwind and temperature profiles from a tethersonde show corresponding bands of differingstability. Internal waves and fossil convection are shown to invalidate attemptsto compare backscatter measurements with theoretical estimates based on local wind and temperature gradients, but during ideal conditions, a qualitative agreementis observed. 相似文献
9.
10.
Fifteen hours of Sodar echoes, collected during the 4th Environmental CEC Campaign at Turbigo, Italy, in September 1979, have been analyzed. We discuss the vertical profiles and the time evolution of the second and third statistical moments of the vertical component of wind velocity, measured at a rate of one height-profile every 6 s for a height range of 1000 m and a vertical resolution of 29 m. We also analyze the power spectra of the vertical velocity. 相似文献
11.
T. Travouillon M. Schöck S. Els R. Riddle W. Skidmore 《Boundary-Layer Meteorology》2011,141(2):289-300
In the second part of this study, we compare both the wind speed and turbulence given by the Sodars with independent sets
of measurements. In the case of the wind speed we compare the lowest Sodar data bin with a sonic anemometer located on a 7-m
tower. The agreement between the two instruments was convincing with a regression slope near unity. The integrated turbulence
measurements of the Sodars are compared with those obtained with a combined multi-aperture scintillation sensor and differential
image motion monitor (MASS/DIMM) unit. It was found that the Sodars are indeed capable of quantitatively measuring optical
turbulence, and agree with the MASS/DIMM measurements with a correlation coefficient of approximately 80% and a regression
slope within 10% of unity. Additional acoustic noise in the Sodar data was identified using this comparison and removed from
the data. 相似文献
12.
Estimates from semiempirical models that characterize surface heat flux, mixing depth, and profiles of temperature, wind, and turbulence are compared with observations from atmospheric field studies conducted in Colorado, Illinois, Indiana, and Minnesota. Sodar observations are compared with tower measurements at the Colorado site, for wind and turbulence profiles. The median surface heat flux, as calculated using surface-layer flux-profile relationships and an energy budget model, was consistently overestimated by 20 to 80%. Several mixing-depth models were evaluated: (1) integration of the hourly surface heat flux and friction velocity, (2) solving for the time rate of change of profiles of virtual potential temperature, and (3) an interpolation scheme used by the U.S. Environmental Protection Agency in regulatory dispersion models. For the late afternoon, 80 to 90% of the estimates from the first and third models were within 40% of the observed values. For the morning hours after sunrise, all were less accurate. Temperature estimates from surface-layer flux-profile relationships compared well with observations within the mixed layer, but were too low for the inversion layer aloft. Wind profiles were derived using surface-layer flux-profile relationships, a windprofile power-law based on Pasquill stability category, and sodar measurements. The sodar measurements were superior to both types of model estimates. Turbulence profiles were derived from sodar measurements and from semiempirical similarity relationships based on mixing depth and Obukhov length. The scatter in the comparisons with the sodar observations is twice that seen in the comparisons with empirical profile relationships. Overall, it appears that uncertainty of as low as 20 to 30% in the characterization of the diffusion meteorology is the exception rather than the rule.On assignment from the National Oceanic and Atmospheric Administration, U. S. Department of Commerce.Disclaimer: Although the research described in this article has been supported by the United States Environmental Protection Agency, it has not been subjected to Agency review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. 相似文献
13.
Under the assumption of a geostrophic wind varying exponentially with height, profiles of four turbulence characteristics (Reynolds stress, eddy diffusivity, momentum mixing length, and energy dissipation rate) are evaluated for three cases of quasi-steady wind profile observations under near-neutral boundary layer conditions. These cases occurred during the Wangara Experiment organized by CSIRO at Hay, N.S.W., Australia, in 1967. It is shown that mean vertical motion and surface friction velocity significantly influence the evaluated profiles of the turbulence characteristics.This study was done while Zhang visited the Department of Meteorology, University of Wisconsin, from the Department of Meteorology, Nanjing University, China, and was completed when Zhang was affiliated with the National Center for Atmospheric Research.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
14.
In this study,cloud base height(CBH) and cloud top height(CTH) observed by the Ka-band(33.44 GHz) cloud radar at the Boseong National Center for Intensive Observation of Severe Weather during fall 2013(September-November) were verified and corrected.For comparative verification,CBH and CTH were obtained using a ceilometer(CL51) and the Communication,Ocean and Meteorological Satellite(COMS).During rainfall,the CBH and CTH observed by the cloud radar were lower than observed by the ceilometer and COMS because of signal attenuation due to raindrops,and this difference increased with rainfall intensity.During dry periods,however,the CBH and CTH observed by the cloud radar,ceilometer,and COMS were similar.Thin and low-density clouds were observed more effectively by the cloud radar compared with the ceilometer and COMS.In cases of rainfall or missing cloud radar data,the ceilometer and COMS data were proven effective in correcting or compensating the cloud radar data.These corrected cloud data were used to classify cloud types,which revealed that low clouds occurred most frequently. 相似文献
15.
We examine the influence of a modern multi-megawatt wind turbine on wind and turbulence profiles three rotor diameters ( $D$ D ) downwind of the turbine. Light detection and ranging (lidar) wind-profile observations were collected during summer 2011 in an operating wind farm in central Iowa at 20-m vertical intervals from 40 to 220 m above the surface. After a calibration period during which two lidars were operated next to each other, one lidar was located approximately $2D$ 2 D directly south of a wind turbine; the other lidar was moved approximately $3D$ 3 D north of the same wind turbine. Data from the two lidars during southerly flow conditions enabled the simultaneous capture of inflow and wake conditions. The inflow wind and turbulence profiles exhibit strong variability with atmospheric stability: daytime profiles are well-mixed with little shear and strong turbulence, while nighttime profiles exhibit minimal turbulence and considerable shear across the rotor disk region and above. Consistent with the observations available from other studies and with wind-tunnel and large-eddy simulation studies, measurable reductions in wake wind-speeds occur at heights spanning the wind turbine rotor (43–117 m), and turbulent quantities increase in the wake. In generalizing these results as a function of inflow wind speed, we find the wind-speed deficit in the wake is largest at hub height or just above, and the maximum deficit occurs when wind speeds are below the rated speed for the turbine. Similarly, the maximum enhancement of turbulence kinetic energy and turbulence intensity occurs at hub height, although observations at the top of the rotor disk do not allow assessment of turbulence in that region. The wind shear below turbine hub height (quantified here with the power-law coefficient) is found to be a useful parameter to identify whether a downwind lidar observes turbine wake or free-flow conditions. These field observations provide data for validating turbine-wake models and wind-tunnel observations, and for guiding assessments of the impacts of wakes on surface turbulent fluxes or surface temperatures downwind of turbines. 相似文献
16.
J. Keder 《Meteorology and Atmospheric Physics》1999,71(1-2):133-138
Summary A REMTECH PA2 Doppler Sodar is operated regularly at the Czech Hydrometeorological Institute (CHMI) observatory in Prague,
collocated with a routine rawinsonde sounding system. The Air Pollution Control Division of CHMI utilises the sodar data in
air pollution studies and as an information support for the smog warning system operated in Prague. Besides of the basic software
for echo strength and wind profile evaluation, optional routines for deriving parameters such as inversion and mixing height,
stability class etc. were delivered by the sodar manufacturer. Based on a sufficiently large data set (more than one year)
of synchronous sodar and rawinsonde measurements, an analysis and comparison of inversion and mixing heights provided by both
sounding systems have been accomplished in order to evaluate the correctness and accuracy of sodar estimates of these parameters.
In contrast to the wind speed and wind direction data, for which a satisfactory agreement with other kind of measurements
has been reported by many studies, the results for inversion and mixing height detection were totally disappointing. A direct
applicability of inversion height and mixing height data provided by the REMTECH’s automatic routines in air pollution studies
or smog warning systems is quite problematical with the present “state of the art”.
Received November 3, 1998 Revised April 20, 1999 相似文献
17.
The ability of subfilter-scale (SFS) models to reproduce the statistical properties of SFS stresses and energy transfers over
heterogeneous surface roughness is key to improving the accuracy of large-eddy simulations of the atmospheric boundary layer.
In this study, several SFS models are evaluated a priori using experimental data acquired downwind of a rough-to-smooth transition
in a wind tunnel. The SFS models studied include the eddy-viscosity, similarity, non-linear and a mixed model consisting of
a combination of the eddy-viscosity and non-linear models. The dynamic eddy-viscosity model is also evaluated. The experimental
data consist of vertical and horizontal planes of high-spatial-resolution velocity fields measured using particle image velocimetry.
These velocity fields are spatially filtered and used to calculate SFS stresses and SFS transfer rates of resolved kinetic
energy. Coefficients for each SFS model are calculated by matching the measured and modelled SFS energy transfer rates. For
the eddy-viscosity model, the Smagorinsky coefficient is also evaluated using a dynamic procedure. The model coefficients
are found to be scale dependent when the filter scales are larger than the vertical measurement height and fall into the production
subrange of the turbulence where the flow scales are anisotropic. Near the surface, the Smagorinsky coefficient is also found
to decrease with distance downwind from the transition, in response to the increase in mean shear as the flow adjusts to the
smooth surface. In a priori tests, the ability of each model to reproduce statistical properties of the SFS stress is assessed.
While the eddy-viscosity model has low spatial correlation with the measured stress, it predicts mean stresses with the same
accuracy as the other models. However, the deficiency of the eddy-viscosity model is apparent in the underestimation of the
standard deviation of the SFS stresses and the inability to predict transfers of kinetic energy from the subfilter scales
to the resolved scales. Overall, the mixed model is found to have the best performance. 相似文献
18.
Comparing mixing-length models of the diabatic wind profile over homogeneous terrain 总被引：1，自引：0，他引：1
Alfredo Peña Sven-Erik Gryning Charlotte Bay Hasager 《Theoretical and Applied Climatology》2010,100(3-4):325-335
Models of the diabatic wind profile over homogeneous terrain for the entire atmospheric boundary layer are developed using mixing-length theory and are compared to wind speed observations up to 300 m at the National Test Station for Wind Turbines at Høvsøre, Denmark. The measurements are performed within a wide range of atmospheric stability conditions, which allows a comparison of the models with the average wind profile computed in seven stability classes, showing a better agreement than compared to the traditional surface-layer wind profile. The wind profile is measured by combining cup anemometer and lidar observations, showing good agreement at the overlapping heights. The height of the boundary layer, a parameter required for the wind profile models, is estimated under neutral and stable conditions using surface-layer turbulence measurements, and under unstable conditions based on the aerosol backscatter profile from ceilometer observations. 相似文献
19.
R. L. Coulter 《Boundary-Layer Meteorology》1990,52(1-2):75-91
Velocity and signal intensity data during stable conditions in the nocturnal boundary layer (NBL) were obtained with a minisodar on two consecutive nights with similar mean conditions. There was little turbulence activity during the first night, but during the second night, continuous background Kelvin-Helmholtz waves and instabilities having a 2-min period grew and penetrated above the mean NBL height at approximately 60-min intervals. Enhanced ozone concentrations at the surface occurred during the active periods even though most mean meteorological parameters were unchanged. Vertical profiles of vertical velocity standard deviation, dissipation rate, and temperature variance destruction rate in the NBL were measured and analyzed separately according to levels of turbulence activity. Well-defined differences between inactive and active periods of a factor of two to four were found for each parameter. The temperature structure parameter flux was large and in opposite directions in the upper and lower part of the NBL during active periods of turbulence, but small during other periods. 相似文献
20.
Investigation of the Planetary Boundary Layer in the Swiss Alps Using Remote Sensing and In Situ Measurements 总被引：1，自引：1，他引：0
C. Ketterer P. Zieger N. Bukowiecki M. Collaud Coen O. Maier D. Ruffieux E. Weingartner 《Boundary-Layer Meteorology》2014,151(2):317-334
The development of the planetary boundary layer (PBL) has been studied in a complex terrain using various remote sensing and in situ techniques. The high-altitude research station at Jungfraujoch (3,580 m a.s.l.) in the Swiss Alps lies for most of the time in the free troposphere except when it is influenced by the PBL reaching the station, especially during the summer season. A ceilometer and a wind profiler were installed at Kleine Scheidegg, a mountain pass close to Jungfraujoch, located at an altitude of 2,061 m a.s.l. Data from the ceilometer were analyzed using two different algorithms, while the signal-to-noise ratio of the wind profiler was studied to compare the retrieved PBL heights. The retrieved values from the ceilometer and wind profiler agreed well during daytime and cloud-free conditions. The results were additionally compared with the PBL height estimated by the numerical weather prediction model COSMO-2, which showed a clear underestimation of the PBL height for most of the cases but occasionally also a slight overestimation especially around noon, when the PBL showed its maximum extent. Air parcels were transported upwards by slope winds towards Jungfraujoch when the PBL was higher than 2,800 m a.s.l. during cloud-free cases. This was confirmed by the in situ aerosol measurements at Jungfraujoch with a significant increase in particle number concentration, particle light absorption and scattering coefficients when PBL-influenced air masses reached the station in the afternoon hours. The continuous aerosol in situ measurements at Jungfraujoch were clearly influenced by the local PBL development but also by long-range transport phenomena such as Saharan dust or pollution from the south. 相似文献